Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $81.96   5.320%   $86.3203   $86.32   $86.30   $86.30  
  Purchase #2 $105.76   11.661%   $118.0927   $118.09   $118.10   $118.10  
  Purchase #3 $65.99   7.185%   $70.7314   $70.73   $70.75   $70.70  
  Purchase #4 $87.47   11.546%   $97.5693   $97.57   $97.55   $97.60  
  Purchase #5 $116.78   5.657%   $123.3862   $123.39   $123.40   $123.40  
  Purchase #6 $214.47   8.569%   $232.8479   $232.85   $232.85   $232.80  
  Purchase #7 $56.79   6.847%   $60.6784   $60.68   $60.70   $60.70  
  7 purchase totals = $729.22       $789.6262   $789.63   $789.65   $789.60